1. Field of the Invention
The present invention relates to a paste for electron sources for forming electron sources which emit electrons upon applying of an electric field, electron sources which use the paste for electron sources, and an emissive display device which forms the electron sources into cathode lines.
2. Description of the Related Art
As a type of field emission panel display devices (FED), there has been reported an emissive display device which uses inorganic carbon materials such as carbon nanotubes or carbon nanofibers as electron sources for emitting electrons upon applying of an electric field. For example, an example in which an emissive display device of a nominal 4.5 inch is described in pp. 1134-1137 of SID99 Digest. The electron sources of this type are formed such that, for example, a paste for electron sources which is produced by mixing carbon nanotubes (CNT) and silver (Ag) particles (paste which is produced by mixing the carbon nanotubes in a silver paste) is applied to conductive films of cathode lines by coating or printing and the paste is fixed to the conductive films by heating (baking) in the atmosphere.
However, when the inorganic carbon material paste formed of carbon nanotubes, carbon nanofibers in which silver is mixed is heated in the atmosphere at a temperature not less than 400 degree centigrade, the inorganic carbon material (also referred to as “carbon nanotubes or the like” hereinafter) is oxidized due to a catalytic action of silver and is formed into CO2 (or CO) so that a major portion of the material is dissipated. Accordingly, when the inorganic carbon material is used as electron sources of a display device, the electron source cannot obtain the sufficient electron emission characteristics and it is difficult to constitute electron sources capable of uniformly emitting electrons. Further, the same tendency is recognized with respect to a paste containing other metal such as nickel (Ni) or the like other than silver to greater or lesser degrees.
Accordingly, with respect to the electron sources which are formed of the paste for electron sources which contains the carbon nanotubes or the like and metal, it is necessary to perform heating such as baking of a coating film or a printing film of the paste which is necessary in the manufacture of the display device at a temperature lower than an optimum temperature which is generally necessary in the process or under the non-oxidizing atmosphere. However, heating in the non-oxidizing atmosphere (atmosphere such as vacuum, nitrogen gas, argon gas or the like) can hardly cope with the increase of size of the panel display device due to restrictions imposed on process facilities including a heater. Further, also in baking the paste for electron sources in the non-oxidizing atmosphere, the carbon nanotubes or the like are partially dissipated due to a residual oxidizing gas or gasses generated from the process facilities and hence, the electron emission performance of the electron sources is degraded and this also constitutes one of factors which make the emission of electrons non-uniform.
As a literature which discloses a technique for forming electron sources using a paste for electron sources in which carbon nanotubes or the like and silver are mixed (CNT-Ag paste), New Emitter Techniques for Field Emission Displays written by J. M. Kim et al. (SID 01 DIGEST pp. 304-307) is known. In this literature, the above-mentioned paste for electron sources is subjected to screen printing, electron sources which are baked at a temperature of 350 degree centigrade in the atmosphere are formed, and a substrate on which the electron sources are formed and a counter substrate on which phosphors and anodes are formed is heated and sealed in an argon gas at a temperature of 415 degree centigrade.